Influence of electron emission effectiveness on characteristics of negative corona discharge
To explain the results of experiments with negative corona in Trichel pulse mode it is proposed the assumption about decisive role of photoemission in supply of electrons from cathode. The results of numerical simulations correspond to experimental data and to simplified clear models.
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
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| Цитувати: | Influence of electron emission effectiveness on characteristics of negative corona discharge / O. Bolotov, V. Golota, V. Ostroushko // Вопросы атомной науки и техники. — 2012. — № 6. — С. 208-210. — Бібліогр.: 2 назв. — англ. |
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irk-123456789-1092042016-11-22T03:02:22Z Influence of electron emission effectiveness on characteristics of negative corona discharge Bolotov, O. Golota, V. Ostroushko, V. Низкотемпературная плазма и плазменные технологии To explain the results of experiments with negative corona in Trichel pulse mode it is proposed the assumption about decisive role of photoemission in supply of electrons from cathode. The results of numerical simulations correspond to experimental data and to simplified clear models. Для пояснения результатов экспериментов с отрицательной короной в режиме импульсов Тричела выдвинуто предположение об определяющей роли фотоэмиссии в поставке электронов с катода. Результаты численного моделирования соответствуют экспериментальным данным и упрощенным наглядным моделям. Для пояснення результатів експериментів з негативною короною в режимі імпульсів Тричела запропоновано припущення про визначальну роль фотоемісії у постачанні електронів з катода Результати чисельного моделювання відповідають експериментальним даним та спрощеним наочним моделям. 2012 Article Influence of electron emission effectiveness on characteristics of negative corona discharge / O. Bolotov, V. Golota, V. Ostroushko // Вопросы атомной науки и техники. — 2012. — № 6. — С. 208-210. — Бібліогр.: 2 назв. — англ. 1562-6016 PACS: 52.80.Hc http://dspace.nbuv.gov.ua/handle/123456789/109204 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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Низкотемпературная плазма и плазменные технологии Низкотемпературная плазма и плазменные технологии |
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Низкотемпературная плазма и плазменные технологии Низкотемпературная плазма и плазменные технологии Bolotov, O. Golota, V. Ostroushko, V. Influence of electron emission effectiveness on characteristics of negative corona discharge Вопросы атомной науки и техники |
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To explain the results of experiments with negative corona in Trichel pulse mode it is proposed the assumption about decisive role of photoemission in supply of electrons from cathode. The results of numerical simulations correspond to experimental data and to simplified clear models. |
| format |
Article |
| author |
Bolotov, O. Golota, V. Ostroushko, V. |
| author_facet |
Bolotov, O. Golota, V. Ostroushko, V. |
| author_sort |
Bolotov, O. |
| title |
Influence of electron emission effectiveness on characteristics of negative corona discharge |
| title_short |
Influence of electron emission effectiveness on characteristics of negative corona discharge |
| title_full |
Influence of electron emission effectiveness on characteristics of negative corona discharge |
| title_fullStr |
Influence of electron emission effectiveness on characteristics of negative corona discharge |
| title_full_unstemmed |
Influence of electron emission effectiveness on characteristics of negative corona discharge |
| title_sort |
influence of electron emission effectiveness on characteristics of negative corona discharge |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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2012 |
| topic_facet |
Низкотемпературная плазма и плазменные технологии |
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http://dspace.nbuv.gov.ua/handle/123456789/109204 |
| citation_txt |
Influence of electron emission effectiveness on characteristics of negative corona discharge / O. Bolotov, V. Golota, V. Ostroushko // Вопросы атомной науки и техники. — 2012. — № 6. — С. 208-210. — Бібліогр.: 2 назв. — англ. |
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Вопросы атомной науки и техники |
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2025-07-07T22:42:13Z |
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2025-07-07T22:42:13Z |
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| fulltext |
208 ISSN 1562-6016. ВАНТ. 2012. №6(82)
INFLUENCE OF ELECTRON EMISSION EFFECTIVENESS ON
CHARACTERISTICS OF NEGATIVE CORONA DISCHARGE
O. Bolotov, V. Golota, V. Ostroushko
NSC “Kharkov Institute of Physics and Technology” Kharkov, Ukraine
To explain the results of experiments with negative corona in Trichel pulse mode it is proposed the assumption
about decisive role of photoemission in supply of electrons from cathode. The results of numerical simulations
correspond to experimental data and to simplified clear models.
PACS: 52.80.Hc
INTRODUCTION
Negative corona discharge is widely used in plasma-
chemical techniques, in particular, in ozone synthesis. To
intensify required reactions, it is worthy to use negative
corona in Trichel pulse mode at relatively high voltage
value but to keep discharge from turn to stationary mode.
In the paper [1], there was studied the dependence of
characteristics of pulses on transverse anode dimensions.
It was revealed that for different transverse anode
dimensions the total current dependences on time during
the pulse are approximately the same, but interval
between pulses increases with transverse anode dimension
decrease. Also, a peculiar feature of mentioned discharge
mode is considerable expansion of glow near cathode in
direction transverse to electric field strength lines. And
the common feature of the pulses is very small time of
current pulse front (as small as 1 ns). To make clear the
physical reasons of the observed phenomena the
numerical simulations were carried out. Their results are
presented below.
1. SIMPLE PULSE MODEL
At the beginning, it is worthy to remind Trichel pulse
development. When sufficiently high voltage value is
applied to discharge gap between anode and cathode and
there is some amount of seed electrons in the gap then the
ionization processes begin to develop. In the case of
needle cathode the ionization rate is especially high in the
region close to cathode. As electron mobility is much
greater than ion mobility, the electrons are quickly
removing from the near-cathode region and there are
formed a positive ion cloud near cathode and a negative
ion cloud somewhere farther from cathode (in presence of
attachment). The charge of negative ions cloud makes
electric field strength smaller between the cloud and
cathode. The charge of positive ions cloud makes electric
field strength greater between the cloud and cathode, but
makes the strength smaller beyond the cloud farther from
cathode. The formation of great amount of positive ions
leads to considerable field weakening beyond them, to
considerable decrease of rate of electrons removing from
there, and to forming of plasma, in which the difference
between the densities of particles with different signs
(which determines the charge) is much less, than the
densities themselves. The plasma region is positively
charged, non-compensated charge is disposed in part of
the region closer to cathode, and the plasma region is
expanded to cathode. If the process was based on the
impact ionization and ion-electron emission (without
drawing of photoemission), and if the ionization
coefficient was not dependent on the field strength then
the spatial distribution of positive ions between plasma
region and cathode would be close to exponential one
with increment close to the ionization coefficient and the
plasma region would approach to cathode with the
velocity close to ion drift velocity. In reality, as ionization
coefficient increases with field strengthening, the
steepness of ions spatial distribution increases and the
process of expansion of plasma region to cathode get the
features of ionization wave. The speed of such wave is
determined with the speed of electron removing from the
ionization front and it much exceeds ion drift velocity.
After ionization wave going off, depending on balance
of negative ion forming and removing from cathode the
discharge may come to stationary mode or operate in
pulse mode.
At the beginning let us consider the case when the
applied voltage value is sufficiently great to ensure fast
displacement of negative ions and their small density near
cathode, so that screening influence of negative ions on
the field near cathode is weak, comparatively with
influence of positive ions. In this case, after arrival at the
cathode of the main part of positive ions, the displacement
of rest positive ions with renewal of the field screened by
them earlier leads to intensification of ionization up to the
level, at which the rate of positive ion forming in the gap
compensates the rate of their going out, so that discharge
comes to stationary mode.
Now let us consider the opposite case, when the
applied voltage value is not sufficiently great to ensure
fast displacement of negative ions from the cathode
(whereas positive ions being in much stronger field are
displaced to cathode much faster). In this case, at the time
when displacement of the rest of positive ions to cathode
begins to weaken the field screening, the contribution of
negative ions to field screening turns out to be enough to
ionization decay. And then, to develop new Trichel pulse
it is necessary some displacement of negative ion cloud
farther from cathode, to renew sufficiently strong field
near cathode.
2. SIMULATIONS RESULTS AND
DISCUSSION
The simulations were carried out for the axially
symmetric system in the frames of model, which accounts
only the main processes: ionization, attachment, electron-
ion and ion-ion recombination, drift and diffusion of
charged particles, ion-electron emission and
photoemission from cathode. The voltage value taken in
calculation was corresponding to one characteristic for
Trichel pulse mode near the turn into stationary mode
ISSN 1562-6016. ВАНТ. 2012. №6(82) 209
(approximately 10 kV for 1 cm gap and 50 μm cathode tip
curvature radius).
At the beginning, there were carried out the
calculation with ion-electron emission, but without
photoemission. The pulse mode obtained in calculation
was characterized by time interval between pulses
approximately 100 ns, while in experiment it was 1 μs
and more. The small time between pulses may correspond
to situation when for pulse development it is sufficient the
region length, at least, not much greater than cathode tip
curvature radius, and in which there is strong field
determined with cathode charge; then, to screen the field
effectively, the negative ions had to be situated near the
pulse development region, so, in sufficiently strong field,
and then, the ions, quickly displacing, had to weaken
screening and to create conditions for new pulse
development during short time. Considerable increase of
time between pulses may be achieved in the case when at
the first stage of pulse development the positive ion
density is maximal in the region, where the field in the
empty gap is considerably weaker than at cathode (so, at
the distance from cathode, considerably greater than
cathode tip curvature radius). If the applied voltage value
is small (close to threshold of negative corona ignition) it
is just the case. If the voltage value is great (close to one
corresponding to turn corona into stationary mode) the
increase of length of the near-cathode region necessary
for pulse development may be achieved through decrease
of ion-electron emission coefficient. If ion-electron
emission coefficient was 10−3, as it is usually used in
calculations, then to ensure the process on the base of ion-
electron emission and impact ionization it would be
enough near 10 subsequent ionization acts for which, in
the field strong enough, it is sufficient electron drift
length approximately 50 μm, which for the same or
greater cathode tip curvature radius leads to the
mentioned small interval between pulses. It is worthy to
note that about low effectiveness of ion-electron emission,
in comparing with photoemission, in atmospheric air
conditions, it is written in [2, p. 94].
In view of stated above there were carried out
calculations, in which ion-electron emission was replaced
with photoemission, and for the number of electrons,
which would be emitted from cathode by photons
generated on unit length of electron drift, in the case of
direction of all these photons to cathode, it was taken the
exponential dependence from reciprocal field strength
with the factor 1 cm−1 at exponent. As a result, the
interval between pulses increases up to microseconds and
becomes more close to experimental data. Also, in the
calculations, there were realized some features of the
studied discharge mode mentioned above.
The first such feature revealed in the experiments [1]
is increase of the interval between pulses with decrease of
characteristic transverse anode dimensions. In
calculations with different values of anode tip curvature
radius such tendency was obtained. It deals with field
redistribution in the gap. With decrease of characteristic
transverse anode dimension (which remains much greater
than one of cathode) the field strength increases near
anode and decreases near cathode (for the given voltage
value over all gap), and, in particular, the field in the
region of negative ion cloud weakens, leading to slowing
down of negative ions displacement from the cathode and
making it greater the time interval between pulses.
The second experimental feature of the studied
discharge mode is considerable expansion of glow near
cathode in direction transverse to the field. The spatial
distribution of the charged particles density and the
reactions intensity obtained in the calculations were in
accordance with such glow expansion. There are, at least,
two reasons of such expansion of the region with
intensive electron processes. The first reason is relatively
large distance between cathode and the region, which at
the beginning of pulse development is the region of large
positive ion density (it is situated near the point, in which,
in the case of empty gap, the derivative of reciprocal
ionization coefficient with respect to distance from the
cathode is equal to 1) and then becomes the part of
plasma region closest to anode. The positive charge
weakens the field near the symmetry axis of the system to
a greater degree than it weakens the field far from the
axis, somewhat decreasing transverse variation of the
glow at relevant distance from the cathode, comparing
with that variation, which would be in absence of space
charge. The second reason, which promotes the expansion
of the region of intensive electronic processes in the
transverse direction in calculation results, is replacing of
ion-electron emission with photoemission. If pulse
develops on the base of ion-electron emission and impact
ionization then mutual influence of the processes, which
takes place on different field strength lines, is relatively
small. If there was no transverse diffusion and time
variation of the field then self-consistent multiplication of
charged particles would develop separately on each
strength line, because the electron emitted from the
cathode due to the positive ion impact would move and
form new positive ions on the same strength line, as the
mentioned positive ion. And the relation of the densities
of charged particles even on the very close strength lines
in these assumptions formally may become with time as
large as you like. Diffusion and time variation of the field
of space charge only somewhat diminish the described
sharp spatial variation of the densities. In contrary to ion
motion, the photon motion is not connected with field
strength lines, and the photons generated by electrons in
the region of intensive electronic processes may cause the
emission of electron from any point of cathode surface
(not shading from the point of the photon generation) and
start electron multiplication there. So, the role of
photoemission in transverse expansion of glow is in
supplying of electrons from cathode to different strength
lines independently on ionization intensity and positive
ion density on that strength lines. Being expanded in such
way, the glow to some degree surrounds cathode,
although the distance between cathode and the points with
equal glow intensity farther from symmetry axis
increases, in connection with weakening of ionization
intensity on relevant strength lines.
As an example of calculations results, in the Fig. 1,
there are shown the distributions of electron density near
cathode at instants of pulse development, corresponding
approximately maximal transverse expansion of electrons
near cathode ((a) in the case of only ion-electron emission
account, (b) in the case of only photoemission account).
210 ISSN 1562-6016. ВАНТ. 2012. №6(82)
The third experimental feature of the studied mode is
the common feature of Trichel pulses: the small time
(approximately, 1 ns) of current rise in pulse
development. In the calculations with account of
photoemission this feature also was realized. The
comparatively large time of current rise (approximately,
10 ns) in the calculations with ion-electron emission, but
without photoemission, is mostly determined by the time
necessary for positive ion to come to cathode. In contrary,
the photon after its generation comes to cathode and
causes emission of electron practically instantly, so, in the
calculations with account of photoemission the time of
current rise is mostly determined by the time necessary
for electrons to make the sufficient number of ionization
acts resulting in formation and propagation of ionization
wave, as it was described above.
CONCLUSIONS
So, to explain the experimental data, concerning the
time of current rise during Trichel pulse developing, the
time interval between pulses, and the spatial distribution
of glow near cathode in negative corona discharge under
conditions, which correspond to pulse mode, but are close
to conditions of mode turning into stationary one, in the
present work, it is proposed the assumption about
weakness of ion-electron emission and decisive role of
photoemission in the conditions of the considered
experiments. The numerical simulations having been
carried out gave the results, which are in accordance with
experimental data and simplified clear models.
REFERENCES
1. V.I. Golota, O.V. Bolotov. Anode curvature influence
on characteristics of negative corona discharge under
Trichel pulsed mode. // Problems of atomic science and
technology, 2011, №. 1, Series «Plasma Physics» (17),
p. 113–115.
2. Ju.P. Raizer. Gas discharge physics. Moscow:
«Nauka», 1992 (in Russian).
Article received 06.09.12
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0,4 0,5 0,6 0,7 0,8
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(a) (b)
Electron density distributions near cathode at instants of pulse development, corresponding approximately maximal
transverse expansion of electrons near cathode: (a) in the case of only ion-electron emission account, (b) in the case of
only photoemission account; the lines corresponds to the densities 109, 1010 1011, and 1012 cm-3
ВЛИЯНИЕ ЭФФЕКТИВНОСТИ ЭЛЕКТРОННОЙ ЭМИССИИ НА ХАРАКТЕРИСТИКИ
ОТРИЦАТЕЛЬНОЙ КОРОНЫ
О.В. Болотов, В.И. Голота, В.Н. Остроушко
Для пояснения результатов экспериментов с отрицательной короной в режиме импульсов Тричела
выдвинуто предположение об определяющей роли фотоэмиссии в поставке электронов с катода. Результаты
численного моделирования соответствуют экспериментальным данным и упрощенным наглядным моделям.
ВПЛИВ ЕФЕКТИВНОСТІ ЕЛЕКТРОННОЇ ЕМІСІЇ НА ХАРАКТЕРИСТИКИ НЕГАТИВНОЇ
КОРОНИ
О.В. Болотов, В.І. Голота, В.М. Остроушко
Для пояснення результатів експериментів з негативною короною в режимі імпульсів Тричела запропоновано
припущення про визначальну роль фотоемісії у постачанні електронів з катода Результати чисельного
моделювання відповідають експериментальним даним та спрощеним наочним моделям.
|